AR1820 USB3.0_UC-425_Rev.C+UC-489 Rev.C - exposure (integration) time calculatio

1.Which seller did you purchase the product(s) from?

2.The Model number of the product(s) you have purchased?
3.Which Platform are you using the product(s) on?
Windows PC
4.Which instruction are you following?
5.Has your product ever worked properly?
Works well
6.What problems are you experiencing?
I don’t understand how to calculate the exposure (integration) time. I’m following this document:

but I don’t know how to get the vt_pix_clk_freq_mhz. The document gives an example where the frequency is 80MHz. Is that value fixed for AR1820? If not how can I calculate or where can I read it?

I’m sorry, I’m very new to ArduCam and the AR1820 data sheet seems very unclear to me…
7.What attempts at troubleshooting have you already made?
I have read the camera documentation.
8.How would you like us to help you?
Explain to me (or send some link) how to get th vt_pix_clk_freq_mhz for integration time calculation